The invention relates to a radiolucent orthopedic fixation plate for use with an orthopedic external fixator.
External fixation systems are known in prior art from U.S. Pat. No. 5,062,844. They use orthopedic fixation plates having the shape of rings for use with additional fixator elements. The person skilled in the art knows such rings for example from the Ilizarov apparatus, which is also published as U.S. Pat. No. 4,615,338. Usually several rings are positioned around a limb, comprising e.g. a broken bone. The rings are interconnected by struts to accommodate elements such as posts etc. which are in connection with a wire being connected to a bony structure.
Such an entire system as well as the rings tend to hide the bone fracture during X-ray shooting. The fracture gap with the surrounding callus is an indicator for the doctor to interpret bone healing. When the doctor then shoots an X-ray image to judge the fracture healing, it is frequent that the fixator hides said fracture so that at least a second X-ray image is necessary for proper interpretation. This however increases the patient's radiation exposure, takes more time, is inconvenient and does not improve the quality of the x-ray itself.
Based on this prior art, it is known to use radiolucent fixation elements made from plastic or composite synthetic materials which are radiolucent. Such an external fixation device is known from WO 97/30651. These materials have the advantage of not masking the fracture area in X-ray images. These materials tend to creep over time, decreasing the tension within the fixation device, lowering the stiffness over time, which as a consequence may influence the bone healing. WO 97/30651 uses a core of a resin matrix reinforced with fibers, but the guiding length of the cylindrical holes for attaching connectors is quite short.
US 2004/0167518 suggests providing the rings in a radiolucent material as polycarbonate or carbon fiber. The rings are in cross-section double-T shaped having apertures or holes to provide the attachment points for the connectors in the thinner middle sections. Two separate beryllium rings are provided in the thicker T-ends of the fixator rings to increase stiffness while avoiding X-ray shading. These rings suffer the same problems as the former mentioned prior art.